Abstract
The stools of a human carrier of E. histolytica were studied daily for 215 days to determine (1) the presence of encystment cycle, (2) the development and viability of immature cysts outside of the body, effects of changes in temperature and moisture, (3) the relative proportions of uni-nucleate cysts at various periods of encystment cycle, and (4) correlation, if any, between consistency of stools and number of discharged cysts.
The number of cysts per gram of stool was calculated according to the method previously described 1 and if cysts were very few, according to a modification of Lane's method 2 for counting hookworm eggs. All negative findings were verified by Rivas' modification 3 of ether-acetic acid concentration method, and also by the culture method recently reported. 4 Gram iodin solution was used in determining the number of nuclei present in samples of cysts examined.
Observations. 1. Encystment Cycle. There was a definite cycle of encystment in E. histolytica as has been observed in giardias by Boeck, 5 Kofoid and others 6 as well as by the author. 1 There was an apparent periodicity in appearance of the maximum number of cysts in each cycle, and the durations of such cycles ranged from 8 to 10 days, the average being 9.2 days. The number of cysts fluctuated from day to day with the maximum of approximately 1,250,000 per gram of stool. In most instances a peak in number was followed by a gradual diminution, and this was subsequently followed by a gradual rise until another peak was reached. However, when a negative period (the complete disappearance of cysts from stool) preceded a cycle, there was observed a sudden rise in the number of cysts.
2. Development and Viability of Immature Cysts.
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